Silver halide emulsions containing vinyl sulfone-gelatin derivatives



United States Patent 3,132,945 SILVER HALIDE EMULSIONS CONTAININ VINYL SULFGNE-GELATIN DERIVATIVES William H. Ryan, Carlisle, Mass, assignor to Polaroid Corporation, Cambridge, Mass, a corporation of Delaware No Drawing. Filed July 13, 1960, Ser. No. 42,495 9 Ciaims. (Cl. 96-94) This invention relates to photography and, more particularly, to novel photosensitive elements and processes for the fabrication of same. It is specifically concerned with the preparation of photographic emulsions having silver halide as the sensitive element and wherein the silver halide is prepared in dispersed form in gelatin. The gelatin is in the form of, or is converted during preparation of the silver halide into, a gelatin derivative which derivative comprises the reaction product of certain organic compounds specified hereinafter and gelatin. The thus-prepared gelatin derivative-silver halide dispersion possesses the properties of being coagulated by pH adjustment to form granules or agglomerates of silver halidegelatin. derivative.

The most common method of preparing photographic silver halide dispersions is by reacting a water-soluble silver salt, such as silver nitrate, with at least one Watersoluble halide, such as potassium bromide, preferably together with potassium iodide, in an aqueous solution of a gelatin colloid peptizing agent. The dispersion of silver halide thus formed contains water-soluble salts as a byproduct of the double decomposition reaction, in addition to an unreacted excess of either of the initial salts. It has been considered desirable in the case of photographic emulsions that the water-soluble salts present in the emulsion be reduced in concentration. It has been generally the conventional practice, where gelatin has been used as a protective colloid, to remove the soluble mate rials therefrom by setting the gel dispersion by means of chilling, noodling the so-set dispersion, and Washing the noodles with cold water.

It is one object of the present invention to provide novel photosensitive silver halide gelatin photographic emulsions.

Another object of the present invention is to provide novel methods for the fabrication of silver halide gelatin photographic emulsions.

A further object of the present invention is to prepare certain specified dispersions of silver halides useful for the preparation of photographic silver halide gelatin photosensitive emulsions.

A still further object of the present invention is to prepare certain specified dispersions of silver halides from which water-soluble byproducts may be readily removed.

A Still further object of the present invention is to provide a conventient practical method of preparing washed silver halide dispersions in which the specified dispersing colloid need be but a small percentage of the total composition and comprises the reaction product of gelatin and an organic compound of the type specified hereinafter.

A still further object of the present invention is to provide a method of washing specified silver halide dis removed, thus making for substantially complete removal of the water-soluble impurities therein.

inclusive.

3,132,945 Patented May 12, 19 4 v, Other objects of thepresent invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of ele ments which are examplified in the following detailed disclosure, and the scope of the application of which will be indicated in the-claims.

The term gelatin as utilized herein is intended to signify the art-accepted designation of the photographic colloid binder derived from collagen and comprising a proteinaceous substance. It is also intended to includeany other product substantially identical therewith, as for example, where such product is produced synthetically.

The fact that certain specified derivatives may be prepared from the gelatin employed as a peptizer for preparing dispersions of silver halide and that dispersions of silver halide in those derivatives are acid coagulable and will form silver halide-gelatin derivative granules when the dispersion is adjusted to the proper pH is disclosed in the following United States patents: 2,614,928 and 2,614,929 issued October 21, 1952; and 2,728,662 issued December 27, 1955. This method avoids the limitations which have previously characterized the preparation of washed silver halide dispersions and is valuable for expanding the possible conditions for the manufacture of photographic silver halide emulsions of different speeds, contrast and other photographic characteristics. In addition, this method otters a simple means of preparing emulsions of high silver concentration, which is of value in the manufacture-of thin photographic films or coatings bearing large quantities of silver per unit area. The present invention is specifically concerned with gelatin derivatives prepared by reacting gelatin with specified organic compounds, set out hereinafter, at a pH of 6 to 11 or more. The basic range may be imparted by suitable base may be used, such as ammonium hydroxide or sodium carbonate, as Well as sodium hydroxide and the corresponding potassium compounds. In the upper part of the range, the use of a stronger base, such as sodium or potassium hydroxide, is preferred; The reaction between the gelatin and the organic agent employed takes place within a few minutes and a silver halide dispersion comprising the reaction product, as the peptizing colloid, takes on the character that it may be coagulated, forming silver halide-gelatin derivative granules, upon acidification of the mass to a pH within the range of 2.0 to 4.5, The insoluble material which results consists of silver halide grains enveloped by gelatin derivative and may be washed free of salts and other water-soluble materials which may be present. As these granules readily settle. from the liquid with which they are in contact,

merely decanting the liquid from the granules removes substantially all of the water-soluble salts therefrom. The granules may be subsequently sujected to washing or to redisp'ersing the granules, such as in a solution having a pH at which they will disperse, and again coagulating,

'by lowering the pH, and removing the liquid from the granules thus formed a second time. The coagulation of the silver halide dispersion in the gelatin derivative is effected by acidifying the mass to a pH Within the range of 2 to 4.5, whereby the granules of silver halide and gelatin derivative will separate out.

In carrying out the present invention, the silver halide is prepared in an aqueous solution of gelatin as the eptizer, the gelatin being present in the form of the desired derivative or converted into the gelatin derivative prior to acidification thereof, by imparting a pH of 6 to 11 to the solution and then reacting the gelatin with the particular organic compound employed. The silver halide may be prepared by any of the normal methods for the preparation of silver halide dispersions, such as, for example, by introducing a stream of an aqueous solution of silver nitrate and a stream of an aqueous solution of at least one alkali-metal halide, preferably potassium bromide and potassium iodide, into a constantly agitated solution of the peptizing agent. Instead, however, the gela tin solution may be combined with one of the reactants and the other reactants may be introduced therein with stirring. After the silver halide has been formed and the gelatin has been converted into the desired gelatin deriva tive, any ripening operations considered advisablemay be effected. Acid is then added to the dispersion to lower the pH to a coagulating pH Within the range of 2 to 4.5. The silver halide-gelatin derivative'dispersion forms granules and quickly settles from the liquid portion of the mass. The coagulum thus formed may then be separated from the liquid by any one of several techniques. In the simplest form, the supernatant mother liquor may be removed from the receptacle in which the mass is contained by means of a siphon or by decantation.

For some type'of emulsions, the coagulum may be used directly without further Washing. Where it is desired to further reduce the content of soluble salts which may be present, any one of several methods may be employed. For instance, the coagulum may be rinsed by treatment with cool water, preferably with the pH thereof adjusted to the range of the isoelectric point of the gelatin derivative. The specific number of rinses which is desirable to reduce the salt content may be determined by experiment, but usually in this method 1 to 4 rinses are sufficient. As an alternative method, the coagulum may be redispersed in Water at an elevated temperature using water and a small amount of alkaline material, such assodium' hydroxide or ammonium hydroxide, so that the pH of the mixture is of the order of 6 or higher. The temperature of the solution is raised to approximately 40 C., and the whole is stirred for a few minutes to effect rcdispersion of the coagulum. The gelatin derivative silver halide granules may again be precipitated by the addition of an appropriate acid to reduce the pH to the coagulation point of the derivative. The coagulum will again settle and the separation from the mother liquor is effected as previously described. This redispersion and' coagulation may be repeated as many times as is necessary. As a third method of washing, the coagulurn may be redispersed in an aqueous solution at a pH below 2.0 so as to effect redispersion of the silver halide-gelatin derivative granules. The low pH may be obtained by the addition of a quantity of an appropriate acid, such as sulfuric acid. Recoagulation may then be effected by the addition of a suitable base, such as sodium or ammonium hydroxide, to raise the pH of the solution to the coagulation point of the derivative; The coagulum will settle and the separation of the supernatant liquid is carried out as previously described. The coagulum after the washing operation consists of silver halide, the gelatin derivative, any other Water-insoluble materials which may be present, and a small amount of residual soluble salts dissolved in any water trapped in the coagulum.

In carrying out the method in accordance with the present invention, the silver halide may be first prepared in a normal gelatin'solution according to standard techniques for the preparation of silver halide, and any ripening which may be desired maybe carried out. The pH of the mass is adjusted to a value of approximately 6 to 11 or higher with a suitable base, for instance, sodium hydroxide or potassium hydroxide, and the organic reagent for formation of the gelatin derivative is added in suitable physical form, usually dissolved in a solvent such as water, methanol, acetone, etc. After a suitable time has elapsed for reaction between the reagent and the gelatin, the pH of the mass may be lowered to the coagulation region. In the alternative process, the gelatin derivative may be formed, as set forth above, and the silver halide prepared, according to standard techniques, in the thus formed gelatin derivative. I

The reagents employed for reaction with gelatin consist of organic compounds possessing at least one and not more than two SO CH=CH groups.

In a preferred embodiment the designated organic compound possesses one or more acid groups such as carboxylic or sulfonic groups or derivatives thereof.

In order to avoid undesirable cross linking during formation of the gelatin derivative and the deleterious hardening thereof resultant from cross linking gelatin, the preferred organic compounds possess only one group.

Preferred organic compounds within the generic concept may be represented by the formula:

wherein R is a monovaleht organic radical and may comprise, for example, an acyclic group such as an aliphatic hydrocarbon radical, or a cyclic'group such as anaromatic hydrocarbon radical, an alicyclic radical, or any combination thereof, as well as organic radicals which contain hetero atoms in addition to carbon atoms. The

organic radical chosen provides ballast or ballasting prop- I erties to the resultant gelatin derivatives formed and preferably possess one or more of the previously described acid groups.

The product formed by reaction of the reagent with gelatin is believed to be the result of an addition reaction between the vinyl group or groups of the organic compound possessing adjacent activating sulfonylv groups and the amino groups of the gelatin molecules amino acid.

The resultant predominantly acid polymer notonly precipitates or dissolves at the desired pH conditions,

units.

but also when in solution retains protective and peptizing properties for the silver halide, and when precipitated remains bound to the silver halide in an appropriate form of curd or grain such that settling is rapid and removal of the supernatant liquid can be efiiciently carried out.

Itwill be recognized that the precipitation rate is determined in part by the number of acid groups contained byv the organic compound as well as the number of, size of,

and configuration of the ballasting groups. The acid groups act to enhance the acid properties of the reaction product and thereby provide an increased propensity for insolubilization or precipitation thereof in a strongly, acid medium. The ballast group provides increased molecular weight to the reaction product facilitating precipitation thereof and, when possessed of one or more of the previ ously mentioned acid groups, additionally acts to enhance theacidic properties of the product and the precipitation thereof in anacid medium.

As examples of suitable ballasting groups to. provide an increasein the molecular weight of the gelatin derivative and thereby provide an increased propensity for insolubilization, mention may be made of: acrylic groupsselected is only limited by the fact that the resultant gelatinous polymer must be soluble at a pH of 6 or more and coagulable at a pH of 2 to 4.5 while retaining its silver halide peptizing and protective properties. The range of choice of ballast group or groups from which the specific group or groups are chosen to provide the desired properties, is therefore extensive.

Specific organic compounds for use in the practice of the present invention comprise:

(1) Hardener D II S (trade name of Carbic-Hoechst Corp., New York, N.Y., for vinyl sulfone hardeners) (2) Remazol Red B (trade name of Carbic-Hoechst Corp., New York, N.Y., for a reactive dye contaimng vinyl sulfone groups) (3) o-Vinylsulfonylbenzoic acid (4) 1,3-divinylsulfonyl-benzene (5) l-'nethyl-4-vinylsulfonyl-benzene (6) 1-methyl-3-vinylsulfonyl-benzene (7) l,3-dimethyl-4,6-divinylsulfonyl-benzene (8) 1,3 ,5-trimethyl-4-vinylsulfonyl-benzene (9) 1,3,5,6-tetramethyl-4-vinylsulfonyl-benzene One method for preparing vinyl sulfones, for use in the practice of the present invention,.comprises the procedure set forth in French Patent No. 901,167, dated January 12, 1944. According to the disclosure of this patent aliphatic-fi-hydroxy-ethyl-sulfones and aromatic- ,B-hydroxy-ethyl-sulfones of the formula:

wherein R is an aliphatic or aromatic radical, may be converted, in the presence or absence of an inert solvent, to their sulfuric acid esters which provide the desired aliphatic or aromatic vinyl sulfone upon treatment with alkali.

Another method for preparing vinyl sulfones, for use in the practice of the present invention, comprises the procedure set forth in French Patent No. 901,306, dated January 18, 1944. According to the disclosure of this patent aliphatic-B-halogeno-ethyl-sulfones and aromaticfi-halogeno-ethyl-sulfones of the formula:

wherein R has the same significance as'previously noted, may be treated with dilute alkali toprovide the desired aliphatic or aromatic vinyl sulfone.

Belgian Patent No. 576,882, dated Mar. 19, 1959, discloses the employment of specified aromatic compounds containing at least two vinyl sulfonyl groups to effect hardening of proteins, particularly photographic gelatin.

For the acid which is to be employed for reducing the pH to the coagulation point, any acid may be employed which will give the desired pH to the mass and which will not deleteriously affect the photographic material. Dilute aqueous sulfuric acid has been found to be particularly useful for this purpose. Nevertheless, other acids, such as phosphoric acid, may be employed.

It is apparent that one advantage of the precipitation technique for the preparation of photographic emulsions described herein is that the concentration ofsilver halide in the final emulsion may be adjusted to any desired value without reference to the quantities of water, silver halideand gelatin employed in the initial reaction for the prepa-.

ration of the silver halide dispersion. Thus, concentrated emulsions may be readily prepared. Dried emulsions may be prepared for storage and shipment without any necessity of extensive evaporation of water or reduction of the water content of the dispersed silver halide and without the necessity of using concentrated salt solutions or organic solvents. The coagulum prepared by the use of gelatin derivatives is especially suitable for the preparation of dried emulsions, since it may be obtained in a state nearly free of excess water, and therefore the drying operation is simplified and rendered less expensive. The coagulum may be obtained in a suitable form for the pur- 6 v pose, and the dried emulsion may be readily dispersed in water containing appropriate alkali at any time.

The .invention will be illustrated in greater detail in conjunction with the following specific example which sets out representative preparations of the novel emulsions of this invention, which, however, is not limited to the details therein set forth and is intended to be illustrative only.

The pH of a 12% aqueous gelatin solution was raised to 10 with 10% sodium hydroxide. 7.5 cc. of a 1 to 2% solution of each of Hardener D II S, and Ramazol Red B, in an appropriate solvent (water, acetone, methanol, etc.), was added to a 7.5 cc. aliquot of the aqueous gelatin solution. The mixture was heated at C. for thirty minutes. (With some compounds higher temperatures provide more rapid results.) (During this period it may be necessary to add more alkali to maintain the pH at 10.)

Subsequent to heating, the pH'of the mixture was lowered to 6.0 with 10% sulfuric acid. A solution comprising 60.0 cc. of water, 8.0 grams of potassium bromide and 0.29 gram of potassium iodide was added to the mixture. 9

The resultant mixture was heated to 70 C. and a solution comprising 10 grams of silver nitrate in 80 cc. of water was added with constant mixing.

The resultant mixture was stirred at 70 C. for twenty minutes and then cooled to 10 C. The pH of the mixture was lowered to 3.5 with 10% sulfuric acid and let stand until the gelatin and silver halide precipitated together, leaving a clear or slightly turbid mother liquor. (Precipitation generally occurs promptly but may require fifteen minutes or longer.) The supernatant liquid was decanted and the precipitate was washed with distilled water until the desired pAg or conductivity was attained.

A solution of 8 grams of gelatin in 30 cc. of water was added to the precipitate and the mixture heated at 50 C; for fifteen minutes with stirring. The pH was ad-v justed to 5.7 to 6.

such as nylon; polyesters such as the polymeric films derived from ethylene glycol-terephthalic acid; and cellulose derivatives such as cellulose acetate, t-riacetate, nitrate, propionate, butyrate, acetate-propionate, or acetatebutyrate.

The light-sensitive material of the photographic emulsion comprises a compound of silver, for example one or more-of the silver halides, of which silver chloride, silver bromide and silver. iodide are examples. The preferred silver halide gelatin emulsion comprises a silver iodobromide gelatin emulsion. It will be understood that preferred silver halide gelatin emulsions of varying halide concentration may be advantageously employed.

The emulsions of the present invention may be chemically sensitized by any of the accepted procedures. For example, the emulsions may be digested with naturally active gelatin, or sulfur compounds can be added such as those described in US. Patents Nos. 1,574,944, 1,623,499

and 2,410,689.

The emulsions may also be treated with salts of the noble metals such as ruthenium, rhodium, palladium,.

iridium, and platinum, all of which belong to group VIII of the periodic table of elements and have an atomic weight greater than 100. The salts may be used for sensitizing in amounts below that which produces any substan- 7 tial fog inhibition, as described in U.S. Patent No. 2,448,- 060 and as anti-foggants in higher amounts, as described in U.S. Patents Nos. 2,566,245 and 2,566,263.

The emulsions may also be chemically sensitized with gold salts as described in U.S. Patent No. 2,399,083 or stabilized with gold salts as described in U.S.; Patents Nos. 2,597,856 and 2,597,915.

The emulsions may also be chemically sensitized with reducing agents such as stannous chloride as described in U.S. Patent No. 2,487,850; amines such as diethylene triamine as described in U.S. Patent No. 2,518,698; polyamines such as spermine as described in U.S. Patent No. 2,521,925; or bis-'(B-aminoethyl)-sulfide and its watersoluble salts as described in U.S. Patent No. 2,521,926.

The emulsions may also be stabilized with the mercury compounds of U.S. Patents Nos. 2,728,663, 2,728,664 and 2,728,665.

The emulsions may also be optically sensitized with cyanine and merocyanine dyes as described in U.S. Patents Nos. 1,846,301; 1,846,302; 1,942,854; 1,990,507; 2,112,140; 2,165,338; 2,493,747; 2,493,748; 2,503,776; 2,519,001; 2,666,761; 2,734,900; 2,739,149; and 2,739,964.

The emulsions may also contain speed-increasing-compounds of the quaternary ammonium type as described in U.S. Patents Nos. 2,271,623; 2,288,226; and 2,334,864;

and of the polyethylene glycol type as described in U.S.

Patent No. 2,708,162.

Where desired, suitable anti-foggants, restrainers, accelerators, preservatives, coating aids, and/or stabilizers may be included in the composition of the emulsions.

Hardening agents such as inorganic agents providing polyvalent metallic atoms, especially polyvalent aluminum or chromium ions, for example, potash alum [K Al (SO ),,.24H O] and chrome alum and inorganic agents of the aldehyde type such as formaldehyde, glyoxal, mucochloric acid, etc., the ketone type such as diacetyl, and the quinonetype, may be incorporated in the emulsions according to procedures well known in the art.

As previously signified, the present invention includes photographic silver halide emulsions formed from silver halide-gelatin derivative granules which comprise the reaction product of gelatin with the preferred organic compounds previously described as possessing not in excess of one -SO CH=CH groups and especially those emulsions formulated byredispersing the silver halideg'elatin derivative granules in a gelatin or gelatin derivative protective matrix or vehicle.

The term photosensitive and other terms of similar import are herein employed in the generic sense to describe materials possessing physical and chemical properties which enable them to form usable images when eX- posed to actinic radiation.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a method of preparing washed silver halide dispersions, the steps which comprise mixing together a water-soluble silver salt and at least one water-soluble alkali metal halide salt in an aqueous solution of gelatin, thereby forming a silver halide dispersion, reacting the gelatin with an organic compound of the formula:

said SO -CH=CH radical comprises the sole vinyl-' sulfonyl radical, to thereby form a derivative of said gelatin, which derivative renders the'dispersion coagulablc at a pH within the range of about 2.0 to 4.5, inclusive, coagulating the dispersion by adjusting same to a coagulating pH, thereby forming silver halide-gelatin derivative particles and separating [the thus-formed silver halidevgelatin derivative particles from the liquid portion of the mass.

' 2. A method of preparing a photographic silver halide emulsion which comprises the steps of preparing a silver halide dispersion which comprises mixing together. silver nitrate and at least one alkali metal halide salt, in an aqueous solution of gelatin, thereby forming a silver halide dispersion, reacting the gelatin with an organic compound of the formula:

wherein R is an organic radical selected from the group consisting of monovalent acyclic and cyclic radicals and said lSO -CH=CH radicalcomprises the sole vinylsulfonyl radical, to thereby form a gelatin derivative coagulable at a pH within the range of about 2.0 to 4.5, inclusive, coagulating the dispersion by adjusting same to a coagulating pH, thereby forming silver halide-gelatin ing said separated silver halide-gelatin derivative granules.

prior to mixing thereof withsaid polymer.

5. A method of preparing a photo-graphic silver halide emulsion as defined in claim 2, wherein said organic radical comprises a monovalent aromatic radical of the henzene series.

6. A method of preparing a photographic silver halide emulsion as defined in claim 2, wherein said compound is selected from the group consisting of o-vinylsulfonylbenzoic acid; l-methyl-4-vinylsulfonyl-benzene; 1-methyl- 3-vinylsulfony1-benzene; 1,3,5-trimethyl-4-vinylsu1fonylbenzene; and 1,3,5,6-tetramethyl-4-vinylsulfonyl benzene.

7. A photosensitive silver halide gelatin emulsion comprising, -in combination, silver halide and the reaction product of gelatin and an organic compound of the formula:

wherein R is an organic radical selected from the group consisting of monovalent acyclic and cyclic radicals, and

References Cited in the file of this patent UNITED STATES PATENTS 2,728,662 Yutzy et a1. Dec. 27, 1955 2,994,611 Heyna et al Aug. 1, 1961 FOREIGN PATENTS 872,153 Germany May 11, 1953 

1. IN A METHOD OF PREPARING WASHED SILVER HALIDE, DISPERSIONS, THE STEPS WHICH COMPRISE MIXING TOGETHER A WATER-SOLUBLE SILVER SALT AND AT LEAST ONE WATER-SOLUBLE ALKALI METAL HALIDE SALT IN AN AQUEOUS SOLUTION OF GELATIN, THEREBY FORMING A SILVER HALIDE DISPERSION, REACTING THE GELATIN WITH AN ORGANIC COMPOUND OF THE FORMULA:
 7. A PHOTOSENSITIVE SILVER HALIDE GELATIN EMULSION COMPRISING, IN COMBINATION, SILVER HALIDE AND THE REACTION PRODUCT OF GELATIN AND AN ORGANIC COMPOUND OF THE FORMULA: 